1. Field of the Invention
The present invention relates to a composition for use in the oral cavity, which comprises a phosphoric ester, exhibits a superior action in protecting the tooth surface, is stable, and has a pleasant taste.
2. Description of Background Art
Phosphoric esters (hereinafter referred to as "AP") cause very little irritation, and exhibit a superior effect in restraining the build up of plaque on the tooth and in preventing dental caries by forming a film on the surface of the tooth for improving the tooth's resistance to acidity. Accordingly, the utilization of AP in a composition for use in the oral cavity has been conventionally proposed. For example, a toothpaste containing a salt of monoalkyl phosphate as a foaming agent, which does not change taste or flavor of foods and beverages is disclosed in Japanese Patent Laid-open (kokai) 47542/1978 (U.S. Pat. No. 4,152,421). Japanese Patent Application (kokoku) No. 500061/1979 (U.S. Pat. No. 4,366,146) discloses a toothpaste composition for preventing the formation of spots, which contains a monoalkyl phosphate as a film-forming material. Japanese Patent Laid-open (kokai) No. 200619/1990 (U.S. Pat. No. 5,019,373) discloses an aqueous composition suitable for use as a dentifrice and as a gargle, comprising a medium-chain dialkyl phosphate, a long-chain dialkyl phosphate, and a monoalkyl phosphate. This composition provides superior decay-resistant activity and does not change flavor or taste of foods and beverages. U.S. Pat. No. 4,036,950 discloses a dentifrice containing an abrasive, a cationic germicide, and polyoxyethylenealkylether phosphate.
When actually manufacturing a composition for use in the oral cavity into which AP is blended, a basic compound is used to neutralize the phosphoric acid group. Conventionally, an alkali metal, an alkaline earth metal, or an alkyl amine is used for this purpose. The use of these basic compounds, however, entails the following problems.
Specifically, an alkali metal salt of AP has a high Krafft point, crystallizes in the formulation, and becomes non-uniform, impairing the stability of the product. Accordingly, it is difficult to apply an alkali metal salt to a transparent, uniform type of mouthwash. In addition, an alkyl amine salt of AP and an alkanol amine salt of AP are strongly irritant, even though they have a low Krafft point. Thus, their safety is a problem. Furthermore, the taste of AP is generally unpleasant, leaving a bitter aftertaste.
A basic amino acid salt of AP is a conventionally known compound. For example, in Japanese Patent Laid-open (kokai) No. 180496/1983, an arginine salt of a phosphate and an emulsifier containing this salt are disclosed. In Japanese Patent Laid-open (kokai) No. 319410/1989 (U.S. Pat. No. 5,085,854) a semitransparent emulsified cosmetic composition containing an arginine salt of monoalkyl phosphate, a nonionic surfactant, an oil component, and water is disclosed. However, all of these prior arts merely propose incorporation of an arginine salt of monoalkyl phosphate into cosmetics as an emulsifier. No prior arts disclose the possibility of blending a basic amino acid salt of AP into a composition for use in the mouth cavity.
An object of the present invention is to provide a composition containing AP for use in the oral cavity which exhibits a superior action in protecting the tooth surface, is stable, and has a pleasant taste.
The inventors of the present invention have undertaken painstaking investigations and found that by using a basic amino acid such as arginine or lysine or the like to neutralize an AP it is possible to obtain a composition for use in the oral cavity, of which the Krafft point of the composition is lowered, which is stable without being colored even when stored for a long period of time, and is suitable for use in protecting the tooth surface, and also has an improved taste.